Metal halide high-pressure discharge lamps of this type are used in particular in lighting systems for stage, film and television, where light with color temperatures of between 5000 and 9000 K and very good color rendering in all color temperature ranges is required. More recently, these lamps have also been used in projection technology and effect lighting, albeit with the known limitations in color rendering on account of the short arc spacing.
U.S. Pat. No. 5,323,085 has disclosed mercury vapor high-pressure discharge lamps with halide additions of dysprosium and hafnium. These lamps emit radiation with a color temperature of between 5000 and 9000 K and a general color rendering index Ra of greater than 70, with the color rendering index R9 for the red spectral region reaching values of up to 50.
However, one drawback is that if the hafnium content is too high, these lamps are prone to arc instability. Moreover, when dimming or boosting the lamps, the temperature change in the burner has a considerable influence on the vapor pressure of the rare earth elements, leading to a considerable change in the color temperature and color rendering.